Method and apparatus for suppressing drillstring vibrations

Abstract

Apparatus and methods are described for isolating in a drillstring a device from acoustic noise by introducing between the device and a source of acoustic vibration an noise isolating apparatus, wherein the noise isolating apparatus has adjacent zones of different acoustic impedance. The zones are preferably created by zones of different thickness and designed such that noise suppression occurs in a predetermined range of acoustic frequencies. In a preferred application the apparatus and method is used in combination with drillstring telemetry.

I claim:  
     
       1. A method for suppressing acoustic noise in a drillstring propagating from a source of acoustic vibration towards a telemetry transmitting unit, said method comprising the step of placing between said telemetry transmitting unit and said source of acoustic vibration a noise suppressing section wherein said noise suppressing section comprises adjacent zones of different acoustic impedance such that noise propagation is suppressed in at least one predetermined frequency band, wherein a plurality of drillstring passbands for energy transmission through the drillstring exits due to a periodic structure of the drillstring, said telemetry transmitting unit transmitting telemetry signals to a telemetry receiver at frequencies within a selected drillstring passband, and said predetermined frequency band includes at least a portion of the selected drillstring passband. 
     
     
       2. The method of  claim 1 , wherein the telemetry transmitting unit uses torsional waves for transmitting signals to another location. 
     
     
       3. The method of  claim 1 , wherein the suppressing section comprises a cylindrical base with adjacent zones of varying wall thickness. 
     
     
       4. An apparatus for suppressing acoustic noise in a drillstring propagating from a source of acoustic vibration towards a telemetry transmitting unit, said apparatus comprising: a noise suppressing unit adapted to be placed between the source of acoustic vibration and the telemetry transmitting unit, the suppression unit including adjacent zones of different acoustic impedance such that noise propagation is suppressed in at least one predetermined frequency band, wherein a plurality of drillstring passbands for energy transmission through the drillstring exist due to a periodic structure of the drillstring, said telemetry transmitting unit transmitting telemetry signals to a telemetry receiver at frequencies within a selected drillstring passband, and said predetermined frequency had includes at least a portion of the selected drillstring passband. 
     
     
       5. The apparatus of  claim 4 , wherein adjacent zones of different impedance are generated by zones of different thickness. 
     
     
       6. The apparatus of  claim 4 , wherein the zones are arranged periodically. 
     
     
       7. The apparatus of  claim 4 , essentially consisting of a cylindrical body of steel with a periodic pattern of grooves. 
     
     
       8. The apparatus of  claim 7  wherein the grooves are filled with a second material so as to maintain a uniform inner and outer diameter of the cylindrical body of steel. 
     
     
       9. The apparatus of  claim 4  wherein the telemetry transmitting unit uses torsional waves for transmitting signals to another location, and the noise suppressing unit is adapted to suppress primarily torsional waves in the at least one predetermined frequency band.